Thermal Regulation Passive Device with Micro Capillary Pumped Fluid Loop

ABSTRACT

The device includes an evaporator and a condenser connected by an outer tube in which extends at least one inner tube having one end leading into the condenser and another end connected to an end of a central duct for collecting the vapours of a heat-carrier fluid, in a microporous mass provided in the outer tube and pumping by capillarity the liquid-phase fluid flowing in at least one outer duct between the outer and inner tubes from the condenser to the evaporator, while the vapour-phase fluid flows from the evaporator to the condenser in at least one inner duct inside said at least one inner tube. The invention can be used for the thermal energy transfer from an electronic component or circuit in relation with the evaporator to a cold source in relation with the condenser.

The present invention relates to a purely passive thermal regulation device, comprising at least one heat transfer loop with the flow of a heat-carrier fluid by capillary pumping, of the type also known as a micro capillary pumped fluid loop, and used for cooling heat sources, such as electronic components or sets of components (circuits).

According to the prior art, a heat transfer loop comprises an evaporator intended to extract heat from a heat source and a condenser intended to return the heat to a cold source. The evaporator and the condenser are connected by tubing in which a heat-carrier fluid flows in a liquid state in the cold part of the loop, and in a gaseous state in the hot part of the loop. The device of the invention relates more particularly to fluid loops in which the pumping of heat-carrier fluid is carried out by capillarity (capillary loop). In this type of loop, the evaporator is associated with a fluid reserve in a liquid state, and comprises a microporous mass (also called a wick) carrying out the pumping of the fluid by capillarity. The liquid-phase fluid contained in the reserve associated with the evaporator evaporates in the microporous mass under the effect of the heat originating from the heat source. The gas created in this way is discharged to the condenser, in heat exchange contact with the cold source, where it condenses and returns in liquid phase to the evaporator, in order to thus create a heat transfer cycle.

One of the limitations of such a heat transfer loop in operation lies in the more or less significant quantity of thermal energy that is transferred to the liquid reserve via the evaporator.

A first effect of this parasitic phenomenon is the heating of the liquid flowing in the loop or contained in the reserve of the evaporator. A second parasitic effect is the reduction of the thermal performance of the transfer loop, which is very sensitive to the temperature of the liquid. Such a transfer loop transports almost all of the energy by phase change of the heat-carrier fluid, and requires, in order to operate, several kilogram calories to keep the fluid flowing from the condenser to the evaporator in a liquid state. Even partial heating of the liquid by any means thus very considerably reduces the heat transfer performance of the loop, and can even result in its complete stoppage.

The object of the present invention relates to passive thermal regulation devices with micro capillary pumped fluid loops, intended for the cooling of heat sources such as electronic components and/or circuits. According to the state of the art, such electronic components or circuits are characterized by a small size (thickness of 1 to 2 mm, area of 10 to 100 mm², for example), and high discharge power densities (over 50 W/cm², for example). Furthermore, the temperature variation between the junction of the electronic component or circuit and the housing of said component or circuit is very large (by a factor of 2 to 3) compared with the temperature variation of the housing of the component or circuit and the temperature of a base plate of a board on which the component or circuit is installed.

The use of a heat transfer loop with capillary pumping to fit the size of the component or circuit, known as a micro loop, allows for the temperature difference between the junction of the component or circuit and the base plate of the board on which it is installed to be reduced advantageously, and thus for the reliability of the component or circuit to be increased, by increasing the power dissipated by the component or circuit.

Such a micro capillary pumped fluid loop is characterized in that it has small dimensions (typical thickness of 1 to 2 mm, typical area of 10 to 100 mm²), in order to allow for it to be installed as close as possible to, or even inside, the component or circuit.

A first drawback of the state of the art for producing such a device lies in the fact that the small size of said micro loop promotes the parasitic transfer of heat to the liquid reserve, which significantly reduces the performance of the loop. This drawback is one of the main limitations for the small size of the evaporator of a micro loop according to the state of the art.

For example, a fluid loop device representative of the state of the art is described in U.S. Pat. No. 7,111,394. In this device, as shown diagrammatically in longitudinal cross-section in FIG. 1 and in cross-section in FIG. 2, which are attached, and arranged in a tube 10 sealed closed at both ends, the evaporator 11 is connected to a liquid reservoir 15, and comprises a microporous mass 12 having a generally cylindrical shape, pierced through by a central artery 14 within which flows the liquid phase 19 of the fluid returning from the condenser 16 towards the reservoir 15. Around the artery 14, on the periphery of the microporous mass 12, ducts 13 are pierced, in which is collected vapour 18, resulting from the heat exchange taking place in the evaporator 11, between the mass 12 and the liquid-phase fluid in the reservoir 15, and pumped by capillarity by the microporous mass 12. It is notable that the vapour phase 18 is confined to the periphery of the mass 12, closest to the area where heat exchange occurs between the heat source (for example an electronic component in contact against the outer surface of the tube 10 at the evaporator 11) and the evaporator 11. The vapour phase is thus maintained at a sufficient distance from the central liquid phase, preventing the parasitic heat flows inevitably present in the mass 12 from heating the liquid phase too much and having a negative effect on the efficiency of the loop. The vapour phase collected in the ducts 13 of the mass 12 is guided towards the condenser 16 by the annular gap between the outer tube 10 and an inner tube 17, in one or more portions, connected by one end to the end of the central artery 14 of the mass 12, while its opposite end opens into the condenser 16 and communicates with the annular volume between the tubes 10 and 17, in order to collect the condensates and recycle the liquid phase towards the reservoir 15.

However, if the miniaturization of the device is sought, to an outer diameter of the evaporator 11 of typically 1 to 2 mm, the peripheral ducts 13 will be very close to the inner artery 14 conveying the liquid, even more so as the diameters of the ducts 13 and the artery 14 must be of a sufficient size to ensure a fluid flow rate allowing for efficient transfer of the heat to be discharged. Significant parasitic heat flows from the vapour to the liquid will then inevitably occur, the liquid will heat up and the efficiency of the loop will collapse.

Another drawback of this device representative of the state of the art also arises from the complexity of production, as soon as the miniaturization of the device is desired.

In order to overcome the drawbacks of the state of the art, the invention proposes a device having at least one micro loop that is very simple to produce, limiting these parasitic effects and thus improving the thermal performance of each micro loop. The device according to the invention is also advantageous for fluid loops with larger dimensions and heat transfer capacity.

In order to overcome the above-mentioned drawbacks, the invention proposes a passive thermal regulation device, comprising at least one heat transfer loop with capillary pumping of a heat-carrier fluid, said loop comprising an evaporator having a microporous mass, and a condenser, intended to be in heat exchange relationship with a heat source and a cold source respectively, and tubing connecting the evaporator to the condenser and transporting the heat-carrier fluid essentially in vapour phase from the evaporator to the condenser and essentially in liquid phase from the condenser to the evaporator, the tubing comprising an outer tube, housing the substantially elongated microporous mass, which ensures the flow of the liquid-phase heat-carrier fluid by capillary pumping, which is characterized in that said liquid phase of said fluid is pumped by a least one end of the microporous mass that is facing the condenser, and flows in at least one outer duct delimited between said outer tube and at least one inner tube extending within said outer tube, and the vapour phase of said fluid heated in the microporous mass of the evaporator is collected in a longitudinal central duct made in said microporous mass and discharged by at least one inner duct delimited within said at least one inner tube, said at least one inner tube being connected by one end to an end of said central duct, while the vapour phase is discharged at the other end of said at least one inner tube, at the condenser.

According to a first advantageous embodiment of the device, said outer tube is closed on itself, forming a continuous loop, of which two substantially opposite portions in relation to the centre of said loop are in heat exchange relationship, one with said condenser, and the other with said evaporator and with said microporous mass, housed in said other portion of the outer tube, and passed through over its entire length by said central duct, two inner tubes extending within said outer tube, each of the two inner tubes being connected, by a first end, to one of the two ends of the central duct of said microporous mass respectively, while the second end of each inner tube opens out into said condenser, opposite the second end of the other inner tube so as to connect the inner vapour-phase fluid duct delimited within each inner tube to said at least one outer duct of liquid-phase fluid flowing from the condenser towards the corresponding end surface of said microporous mass.

According to a second particular embodiment, advantageous in terms of simplicity, said outer tube is closed at both ends and both ends are in heat exchange relationship, one with said condenser, and the other with said evaporator and with said microporous mass housed in this end of the outer tube, said liquid phase of said fluid is pumped by the end of the microporous mass facing the condenser, and flows in an outer duct delimited between said outer tube and an inner tube extending within said outer tube and the vapour phase of said fluid heated in the microporous mass of the evaporator is collected in a longitudinal central duct made in said microporous mass and discharged by the inner duct delimited within said inner tube, said inner tube being connected by one end to an end of said central duct, while the vapour phase is discharged at the other end of said inner tube, at the condenser.

In all cases, to facilitate the pumping of the liquid condensed in the condenser and to separate the vapour and liquid phases at this point, it is advantageous that said other end of said a least one inner tube located at the condenser is fitted into an annular microporous mass filling a space delimited within said condenser between said other end of said inner tube and said outer tube.

Moreover, preferably, the liquid condensing in the condenser is drained to said annular microporous mass, preferably along the wall of said outer tube for example by a capillary drain or a microporous mass located along the wall of said outer tube at said condenser.

If the space constraints of the device allow, advantageously, each of the evaporator and the condenser comprises at least one outer sleeve made from a good heat conducting material, said at least one sleeve of the evaporator surrounding, at least partially, a portion of the outer tube housing said microporous mass, and said at least one sleeve of the condenser surrounding a portion of the outer tube in which at least one inner duct releases the vapour-phase fluid towards said at least one outer duct.

In these cases, at least one of the outer sleeves of the evaporator and the condenser comprises at least one base plate made from a good heat conducting material whereby said sleeve is intended to be placed in heat exchange relationship with a source that is respectively hot or cold.

In these different embodiments, the walls of said at least one inner tube are made from at least one thermally insulating material, preferably a synthetic material known as plastic, in order to ensure good thermal insulation between the vapour phase flowing in the inner tube and the liquid phase flowing in the duct(s) located between the inner and the outer tubes.

In an advantageous embodiment, said at least one inner tube for discharge of the vapour extends into said microporous mass in order to provide greater sealing between the vapour and liquid phases of the fluid at the microporous mass.

Advantageously, said inner tube comprises in its outer wall at least one capillary drain defined for example by at least one substantially longitudinal groove, at least on that portion of said inner tube that extends into the microporous mass, so as to convey the liquid phase deep within said microporous mass by capillarity.

Advantageously in all cases, the outer wall of said at least one inner tube comprises capillary drains defined for example by substantially longitudinal grooves extending preferably over the entire length of said tube.

According to another advantageous variant embodiment, in addition to said microporous mass, the outer wall of said at least one inner tube is in contact with the inner wall of said outer tube, except at the at least one capillary drain defined by at least one substantially longitudinal groove made in the outer surface of said inner tube and defining at least one outer duct conveying the liquid phase of said fluid.

Said microporous mass advantageously has a substantially cylindrical outer shape, together with the portion of said outer tube that houses it without radial play.

In order to retain good efficiency of the loop while avoiding parasitic phenomena, said evaporator has an area intended to be in heat exchange contact with said heat source, a dimension of which along the axis of said outer tube is significantly smaller than the length of said microporous mass, preferably of the order of half of said length of said mass.

Moreover, said microporous mass has a length that is approximately 2 to 15 times greater than its diameter so as to create a significant reserve of liquid distant from the area of heat exchange with the heat source.

Advantageously moreover, said outer tube is in heat exchange contact with said microporous mass over the entire outer surface of said mass apart from one or both of its longitudinal end surfaces.

In a simple embodiment, said outer tube has a constant-diameter cross-section.

Moreover, the outer tube is advantageously made from a good heat conducting material, at least in one portion in heat exchange relationship with said microporous mass, and in another portion in heat exchange relationship with said condenser or constituting the latter.

In practice, said outer tube is metal, preferably stainless steel.

According to a simplified structure, said outer tube and said at least one inner tube are cylindrical with a circular cross-section, the diameter of said at least one inner tube being approximately half of the diameter of the outer tube.

The invention also relates to the application of a passive thermal regulation device with at least one heat transfer loop according to the invention as defined above, to the transfer of thermal energy from a heat source, such as an electronic component or set of components, in heat exchange relationship with the evaporator, to a cold source in heat exchange relationship with the condenser.

Further characteristics and advantages of the invention will become apparent from the non-limitative description given below of specific examples of embodiments described with reference to the attached drawings, in which:

FIG. 1 is a longitudinal cross-sectional view of an example fluid loop device according to U.S. Pat. No. 7,111,394;

FIG. 2 is a cross-sectional view at the microporous mass of the example in FIG. 1, according to U.S. Pat. No. 7,111,394, FIGS. 1 and 2 having already been described above,

FIG. 3 is a diagrammatic longitudinal cross-sectional view of a fluid micro loop device according to the invention;

FIG. 4 is a longitudinal cross-sectional view on a larger scale of a detail of the device in FIG. 3 around the microporous mass;

FIG. 5 is a cross-sectional view along V-V in FIG. 4 at the evaporator;

FIG. 6 is a view similar to FIG. 3 of a simplified micro loop fluid device variant according to the invention;

FIG. 7 is a diagrammatic longitudinal cross-sectional view, on a smaller scale than FIG. 3 and limited to the portions of the device including the evaporator and the condenser, of a variant embodiment of the device in FIG. 3;

FIG. 8 is a cross-sectional view along VIII-VIII in FIG. 7,

FIG. 9 is a diagrammatic longitudinal cross-section at the evaporator, of another variant embodiment of the device of the invention; and

FIG. 10 is a cross-sectional view along X-X in FIG. 9.

A first embodiment of the passive thermal regulation device of the invention is illustrated in FIG. 3, showing a longitudinal cross-section of an entire double micro loop, FIG. 4 showing a longitudinal cross-section of the area of the loop encompassing the evaporator and FIG. 5 showing a cross-section of the centre of the evaporator. All of the numerical values and technical characteristics relating to the materials and fluids given below are for information only. This information is compatible with the industrial production of the invention with the existing equipment of the state of the art.

In this embodiment, the device with micro capillary pumped fluid loop 20 comprises an outer tube 21 having walls made from a good heat conducting material, advantageously metal, for example made from stainless steel, that is for example a cylindrical tube with a circular cross-section, with a constant outer diameter of 2 mm and a wall thickness of 0.2 mm. This tube 21 is closed on itself in a continuous loop to form a closed circuit, in which flows a heat-carrier fluid, which can typically be ammonia, water, or any other diphasic fluid. A filling tube of the micro loop connected to the main tube 21 is not shown in FIG. 3 in order to simplify the diagram.

In an evaporator 22, a microporous mass or wick 23, having a cylindrical shape with a circular cross-section, is positioned without radial play inside a section of the tube 21. The outer diameter of the microporous mass 23 is therefore 1.6 mm and its length is for example 20 mm. The microporous mass can be a single block of the same composition, with pores the diameter or principal dimension of which is of the order of 1 to 10 μm. In a variant embodiment, the pores can optionally have variable dimensions, for example ranging from large pores in the axial end areas 23 b of the wick 23 to promote the capillary pumping of the liquid and its insulation vis-à-vis parasitic heat flows originating from the heat source 27 and the central area 23 a of the wick 23, to small pores in the central area 23 a of the wick 23, where the vaporization of the pumped liquid fluid takes place, as explained below.

The evaporator 22 also comprises a cylindrical sleeve 24, also with a circular cross-section, that is passed through axially and without significant radial play by the portion of the outer tube 21, which surrounds the microporous mass 23, the sleeve 24 being made from a good heat conducting material, preferably metal, and, optionally, of the same type as the outer tube 21, i.e. stainless steel, the length of the sleeve 24 along its axis, which is also that of this section of the tube 21 and the microporous mass 23 (as these three components are substantially coaxial) being about half the length of the mass 23.

Thus, the sleeve 24 is in a good heat exchange relationship with the outer tube 21, which is also in a good heat exchange relationship with the microporous mass 23 over the entire outer surface of the latter apart from its two longitudinal end faces 23 c connected to each other by a cylindrical central duct 25 with a circular cross-section, which passes right through the mass 23.

Moreover, as shown in FIG. 5, the sleeve 24 of the evaporator 22 is secured to a base plate 26, and preferably of a single piece with the latter, the axial dimension of which can preferably be the same as that of the sleeve 24, and which constitutes an area via which the evaporator 22 can be placed in heat exchange relationship with a heat source 27, shown diagrammatically in dotted lines in FIGS. 3, 4 and 5 by a parallelepipedal body, which can be an electronic circuit or component to be cooled, and against which the base plate 26 is in plane contact promoting heat transfers by conduction from the heat source 27 to the base plate 26 and therefore to the sleeve 24, itself in a good heat exchange relationship, as already mentioned above, with the microporous mass 23, as a result of the coaxial mounting without radial play of the mass 23 in a section of the tube 21, and of the latter in the sleeve 24 of the evaporator 22.

The base plate 26 of the evaporator 22 in thermal contact with the heat source 27 thus has a dimension of approximately 10 mm along the axis of the outer tube 21, and the base plate 26 is centred in relation to the microporous mass 23, such that both the areas and end faces 23 b and 23 c of the microporous mass 23 are separated from the central area 23 a of heat exchange with the heat source 27.

To improve the heat exchanges at the contact surfaces, the microporous mass 23 is attached to the inner cylindrical wall of the tube 21 and the outer cylindrical wall of the tube 21 is itself attached to the inner cylindrical wall of the sleeve 24 of the evaporator 22 by any means that ensures the best thermal contact possible, for example by gluing, sintering or any other means.

The device also comprises a condenser 28 mounted, in this example, on a straight section of the outer tube 21 that is opposite the straight section of tube 21 passing through the evaporator 22, in the loop formed by the outer tube 21 and in relation to the centre of the loop. As for the evaporator 22, the condenser 28 comprises a cylindrical sleeve 29, made from a good heat conducting material, preferably metal, which is in good heat exchange contact with the section of tube 21 that passes through it, on the one hand, and on the other hand, with a cold source 30, shown diagrammatically in FIG. 3 by a dotted rectangle, and which can be a heat sink, for example a metal component of a supporting structure.

As for the evaporator 22, the sleeve 29 of the condenser can optionally comprise a base plate (not shown) promoting heat exchange contact with the cold source 30 and, as in the evaporator 22, steps can be taken to promote thermal contact between the sleeve 29 of the condenser 28 and the portion of outer tube 21 passing through it.

The device also comprises two inner tubes 31, which in this example, are substantially identical to each other, cylindrical with a circular cross-section, with a constant diameter that is approximately half that of the outer tube 21, and which are made from a thermally insulating material, for example a synthetic material known as plastic.

For example, their outer diameter is 1 mm and their wall thickness is 0.1 mm.

Each of these inner tubes 31 has a first end 32, by which it is fitted and fixed into one respectively of the two longitudinal ends of the longitudinal central duct 25, for example having a diameter of 0.8 mm, of the microporous mass 23, as shown in more detail in FIG. 4, so that each of the inner tubes 31 is connected to the microporous mass 23 by fitting its first end 32 into one respectively of the two longitudinal end areas 23 b of the mass 23. The connection of the inner tubes 31 with the microporous mass 23 must be sealed in order to prevent the liquid and vapour phases from coming into contact at this point.

The second end 33 of each of the two inner tubes 31 extends into the section of the outer tube 21 passing through the sleeve 29 of condenser 28, into which each second end 33 opens out freely opposite the second end 33 of the other inner tube 31, so that the outer tube 21 and the two inner tubes 31 delimit an annular outer duct 34, inside the outer tube 21 and outside the inner tubes 31, and two inner ducts 35 each inside one respectively of the two inner tubes 31.

In order to separate the vapour phase from the liquid phase generated by condensation in the condenser 28, it can be advantageous to tightly fit the end 33 of each of the inner tubes 31 into one of the two annular microporous masses 38 respectively, each filling an annular space delimited between a portion of the corresponding end 33 and a radially peripheral portion of the outer tube 21 in the condenser 28, the function of which is to capture the liquid phase by capillarity at the condenser 28, while preventing the vapour phase from returning in the outer duct 34. Advantageously, it is possible to extend these annular microporous masses 38 along the inner wall of the outer tube 21 at the condenser 28 in order to pump the liquid more efficiently at this point. This capillary drain can be produced by a cylindrical sleeve 39 of microporous mass, having a radial thickness less than that of the masses 38, and connecting them to each other, and optionally of a single piece with the two masses 38 in a microporous monolithic component 40. As a variant, the cylindrical sleeve 39 can be replaced by a metal sleeve with grooves extending from one to the other of its axial ends, on its inner surface, each groove forming a capillary drain.

This device operates as follows. The base plate 26 of the evaporator 22 collects heat generated by the heat source 27 and transmits it, by conduction, to the section of outer tube 21 in contact with the microporous mass 23.

The microporous mass 23, heated in this way by the section of outer tube 21 surrounding it, heats essentially in its central area 23 a the liquid-phase fluid originating from the outer duct 34, which has been sucked up and pumped by capillarity by the microporous mass 23, at its longitudinal end areas 23 b which are sufficiently long axially to thermally insulate the liquid in the outer duct 34, which can thus contain a liquid reserve close to the wick 23. Each axial end face 23 c of the wick 23 where the liquid phase arrives is also separated from the central area 23 a of the wick which is in heat exchange with the heat source 27. In other words, each end area 23 b of the microporous mass 23 keeps the liquid away from the hot central area 23 a where vaporization takes place. The liquid-phase fluid pumped into the microporous mass 23 is vaporized in the central area 23 a and the vapour is collected in the central duct of the mass 23, whence the vapour-phase fluid is discharged towards each of the two inner ducts 35, which guide the vapour-phase fluid to the ends 33 of the inner tubes 31 into the condenser 28, where the vapour of this fluid condenses, and the liquid condensates are pumped by the microporous masses 38, 39 and guided by the outer duct 34 from the condenser 28 towards the evaporator 22, to ensure the liquid-phase fluid supply of the microporous mass 23, via its two longitudinal end faces and areas 23 b and 23 c, as already mentioned above.

Thus, the liquid-phase fluid moves along the arrows 36 in FIG. 3, in the outer duct 34, from the condenser towards the two longitudinal ends 23 c of the microporous mass 23 of the evaporator 22, while the vapour generated by the evaporator 22 during the operation of the loop is collected in the central duct 25 of the mass 23, in the central area 23 a of the latter, and discharged by the two longitudinal end areas 23 b of the mass 23 in the inner ducts 35, in which the vapour-phase fluid moves along the arrows 37 in FIG. 3, from the evaporator 22 to the condenser 28, where the ducts 35 communicate with the outer duct 34 providing the return of liquid-phase fluid to the evaporator 22 via the microporous component 40. The thermally insulating material of the inner tubes 31, which separate the vapour phase from the liquid phase, has the advantage of limiting the heat exchanges between the two fluid phases flowing in the double loop.

Due to the considerable length of the microporous mass 23 relative to its diameter and relative to the dimensions of the heat collecting area in the evaporator 22, the liquid-phase fluid reserve contained in the outer duct 34, inside the outer tube 21 and on each side of the microporous mass 23, is sufficiently far away from the heat source 27, despite the small size of the evaporator 22, to minimize the parasitic flow of thermal energy towards the liquid reserve, which allows for the improvement of the thermal performance of the device.

It must be noted that, in the device as presented above, the evaporator 22 and the condenser 28 each comprise a thermally conductive sleeve 24 or 29, but, as variants, as described below with reference to FIGS. 7 to 10, the sleeve can be constituted directly by a section of the outer tube 21 made of a good heat conducting material, and which, also as a variant, can be made from such a good heat conducting material only on the two sections of the outer tube 21 that, for one, surrounds the microporous mass 23 and for the other, is surrounded by the sleeve of the condenser 28 or itself constitutes the sleeve.

FIG. 6 shows a simplified variant of the device of the invention, comprising an elementary micro capillary pumped fluid loop, in which is located an outer tube 21 that connects an evaporator 22 to a condenser 28, while being engaged and fixed by its two closed longitudinal ends in sleeves 24 and 29 respectively of the evaporator 22 and the condenser 28. The axial end portion of outer tube 21 engaged in the sleeve 24 of the evaporator 22 surrounds the cylindrical microporous mass 23 which, in this example, has a longitudinal central duct 25 for collecting vapour, which only opens out by the longitudinal end 23 c of the mass 23 that is facing the condenser 28, and into which is fitted and fixed one end of a thermally insulating inner tube 31, extending within the thermally conductive outer tube 21. The other end 33 of the inner tube 31 is fitted into an annular mass 38 of another monolithic microporous element 40′ making it possible to separate the liquid phase from the vapour phase at the condenser 28, and opens out inside the end portion of the outer tube 21 housed in the sleeve 29 of the condenser 28 and lined with the microporous component 40′, in order to connect the duct 35, within the inner tube 31 and guiding the vapour-phase fluid from the output of the duct 25 of the mass 23 to the condenser 28, to the annular outer duct 36 guiding the condensed liquid-phase fluid from the condenser 28 to the microporous mass 23 of the evaporator 22, which pumps the liquid by capillarity and vaporizes it under the effect of the heat received from the heat source 27, in a heat exchange relationship with the evaporator 22, the heat discharged from the heat source 27 being transferred by the condenser 28 to the cold source 30, when the fluid loop is operating, in the same conditions as described above for the example in FIGS. 3 to 5.

The microporous element 40′ comprises the annular mass 38, similar to one of the two annular masses 38 in FIG. 3 and occupying the radial space between the end 33 and the outer tube 21, and extended towards the closed end of the outer tube 21 by an axial thin microporous tube 39′ and a radial thin microporous disc 41 against the base closing the end of the tube 21, the microporous tube 39′ and disc 41 constituting a capillary drain that facilitates the supply to the mass 38, of liquid condensed in the condenser 28 within the component 40′, and thus guided by capillary pumping into the outer duct 31.

In FIG. 6, the tubes 21 and 31 are straight, but they can be bent in their central portions between the evaporator 22 and the condenser 28, in order to adapt the device to the volume available in the immediate environment of the heat source 27 and/or cold source 30.

FIGS. 7 and 8 show a variant embodiment of the device according to FIGS. 3 to 5, in which the outer sleeves of the evaporator 22 and the condenser 28 are removed and each replaced by a respective section of the outer tube 21, having constant outer and inner diameters over its entire length. Similarly, the outer and inner diameters of the inner tubes 31 are constant over their entire length, the inner diameters of the inner tubes 31 and of the central duct 25 of the microporous mass 23 being equal. For the rest, the arrangement of the evaporator 22 and of the condenser 28 is essentially the same as in FIGS. 3 and 4, so that the same references denote the same components. However, in this variant, capillary drains 42 in the form of grooves are made in the outer surface of each inner tube 31 at least at the end portion 32 of the inner tube 31 which is fitted into the microporous mass 23 so as to convey the liquid deep into said mass 23. A large number of grooves 42 can be made on the entire outer periphery of each inner tube 31, so as to optimize the fluid pumping flow rate (see FIG. 8). These capillary drains 42, in the form of grooves that narrow at their opening on the outer surface of the inner tube 31, thus having a cross-section promoting the capillary pumping of the liquid used in the loop, can extend over the entire length of the corresponding inner tube 31 up to the condenser 28, in the end 33 of the tube 31, as shown in the upper half cross-sections in FIGS. 7 and 8. However, the grooves do not penetrate deeper than half the thickness of the wall of the inner tube 31, so as to maintain good thermal insulation between the vapour and liquid phases of the fluid. In this example in FIGS. 7 and 8, the end 32 of each inner tube 31 extends into the microporous mass 23 over an axial distance of one to several times the diameter of the outer tube 21, so that the grooves defining the capillary drains 42 guide the liquid deep within the mass 23 by capillarity.

As a variant, the grooves of the drains 42, which can be parallel to the axis of the tube 31 or helical, are filled with a microporous material, the pores of which have dimensions greater than those of the pores of the microporous mass 23, and substantially equal to or greater than the pores of the microporous mass 40.

In a further variant shown in the lower half cross-sections in FIGS. 7 and 8, the capillary drains 42 in the form of grooves can be replaced, at least at the evaporator 22, but preferably over the entire length of each inner tube 31, by another annular microporous mass 43 surrounding the inner tube 31, this other microporous mass 43 being capable of having a different composition from the main microporous mass 23 used for the evaporation of the fluid, for example having pores with a significantly larger average diameter, typically by a factor of 2 to 10, than the average diameter of the pores of the main microporous mass 23 and substantially equal to or slightly greater than that of the pores of the microporous mass 40. Microporous capillary drains 43 are thus produced.

FIGS. 9 and 10 show respectively, in a longitudinal cross-section at the evaporator 22 and a transverse cross-section between the latter and the condenser 28, two further variant embodiments of the device according to the invention. As a variant according to the upper half cross-sections in FIGS. 9 and 10, the outer wall of each inner tube 31 is in contact with the inner wall of the outer tube 21, from the longitudinal ends of the microporous mass 23 of the evaporator 22 to the condenser 28, except at the narrowed openings of a number of outer ducts 34′, each of which has a small cross-section, in this example in the shape of a droplet, made in the outer surface of the inner tubes 31 in which numerous grooves 42′ are made over the entire periphery of each tube 31. These longitudinal or helical grooves 42′, or others, each defining an outer duct 34′, are only made in substantially the outer radial half of the thickness of the wall of each inner tube 31, so that the liquid phase flowing in these grooves 42′—outer ducts 34′ remains well insulated thermally from the vapour phase flowing in the inner ducts 35 inside the tubes 31.

For the rest, the evaporator 22 exhibits substantially the same arrangement of the wick 23 as in FIG. 7, with however, a stepped cut-out in the ends 33 of the inner tubes 31 where they are fitted into the microporous mass 23, when the capillary drains formed by the outer ducts 34′ extend into the microporous mass in order to supply liquid to the end surfaces 23 c of the end areas 23 b of the mass 23, while the massive inner radial annular half of each inner tube 31 abuts an axial end surface of the central area 23 a of the mass 23. At the condenser (not shown) substantially the same arrangements as in FIG. 7 are present, with the ends of the grooves 34′ of the tubes 31 that open out against the annular microporous mass 38, another cylindrical central microporous mass optionally being capable of being mounted between the two annular masses 38.

As a variant, it is possible to fill the outer ducts 34′ with a microporous material having pores with average dimensions greater than those of the pores of the mass 23, at least in the end portions 32 and optionally 33, of the tubes 31, at the evaporator and the condenser, or even over the entire length of the tubes 31.

Also as a variant, as shown in the lower half cross-sections in FIGS. 9 and 10, the outer ducts 34′ forming capillary drains can be replaced by another annular microporous mass 43′, surrounding the ends 32 and/or 33, or even each tube 31 in its entirety, the radial thickness of which is reduced to substantially its inner radial half, the average dimensions of the pores of the annular mass 43′ being greater than those of the pores of the mass 23 and substantially equal to or slightly greater than that of the microporous mass of the condenser. Outer ducts arranged in capillary drains 43′ are thus produced. It is also possible to produce a single-loop device having a single inner tube 31 according to FIG. 6 with outer ducts 34′ being produced, acting as capillary drains and defined by grooves 42′ in the outer surface of the inner tube 31 in contact with the inner surface of the outer tube 21 as in FIGS. 9 and 10, it then being possible to provide a tube for filling with liquid fluid in the axial extension of the condenser 28, on the side opposite the evaporator 22.

In embodiments having double loops, as in FIGS. 3, 7 and 9, the filling tube opens out “radially” or perpendicularly into a portion of the outer tube 21 located between condenser and evaporator 22.

Given the small dimensions of a device with at least one fluid micro loop according to the invention, such a device can be advantageously applied to the transfer of thermal energy from a heat source 27 with a high thermal power density but small dimensions, such as an electronic component or circuit, placed in heat exchange relationship with the evaporator of the device of the invention, to a cold source 30 placed in heat exchange relationship with the condenser of said device. 

1. A passive thermal regulation device, comprising at least one heat transfer loop with capillary pumping of a heat-carrier fluid, said loop comprising an evaporator having a microporous mass, and a condenser, for being in heat exchange relationship with a heat source and a cold source respectively, and tubing connecting said evaporator to said the condenser and transporting said heat-carrier fluid essentially in vapour phase from said evaporator to said condenser and essentially in liquid phase from said condenser to said evaporator, said tubing comprising an outer tube, housing said microporous mass having a substantially elongated shape and, ensuring a flow of said liquid-phase heat-carrier fluid by capillary pumping, wherein said liquid phase of said fluid is pumped by at least one end of said microporous mass which is facing said condenser, and flows in at least one outer duct delimited between said outer tube and at least one inner tube extending within said outer tube, and said vapour phase of said fluid heated in said microporous mass of said evaporator is collected in a longitudinal central duct made in said microporous mass and discharged by at least one inner duct delimited within said at least one inner tube, said at least one inner tube being connected by one end to an end of said central duct, while said vapour phase is discharged at an other end of said at least one inner tube, at said condenser.
 2. The device according to claim 1, wherein said outer tube is closed on itself, forming a continuous loop, two substantially opposite portions of said outer tube, in relation to a centre of said loop, are in heat exchange relationship, one portion with said condenser and the other portion with said evaporator and with said microporous mass housed in said other portion of said outer tube, and passed through over an entire length of said microporous mass by said central duct, two inner tubes extending within said outer tube, each of said two inner tubes being connected, by a first end, with one of two ends of said central duct of said microporous mass respectively, while a second end of each inner tube opens out into said condenser opposite said second end of the other inner tube so as to connect an inner vapour-phase fluid duct delimited within each inner tube to said at least one outer duct of liquid-phase fluid flowing from said condenser towards a corresponding end face of said microporous mass.
 3. The device according to claim 1, wherein said outer tube is closed at both ends which are in a heat exchange relationship, one with said condenser, and the other with said evaporator (22) and with said microporous mass housed in said other end of said outer tube, said liquid phase of said fluid is pumped by said one end of said microporous mass facing said condenser, and flows in said outer duct delimited between said outer tube and said inner tube extending within said outer tube, and said vapour phase of said fluid heated in said microporous mass of said evaporator is collected in a longitudinal central duct made in said microporous mass and discharged by said the inner duct delimited within said inner tube, said inner tube being connected by one end to one end of said central duct, while said vapour phase is discharged at said other end of said inner tube, at said condenser.
 4. The device according to claim 1, wherein said other end of said at least one inner tube located at the level of said condenser is fitted into an annular microporous mass filling a space delimited within said condenser between said other end of said inner tube and said outer tube.
 5. The device according to claim 4, wherein liquid condensing in said condenser is drained to said annular microporous mass, by at least one of a capillary drain and a microporous mass located along a wall of said outer tube at said condenser.
 6. The device according to claim 1, wherein each of said evaporator and condenser comprises at least one outer sleeve made from a good heat conducting material, said at least one sleeve of said evaporator surrounding at least partially, a portion of said outer tube that houses said microporous mass and said at least one sleeve of said condenser surrounding a portion of said outer tube in which said at least one inner duct releases said vapour-phase fluid towards said at least one outer duct.
 7. The device according to claim 6, wherein said at least one outer sleeves comprises at least one base plate made from a good heat conducting material whereby said sleeve is intended to be placed in heat exchange relationship with one of a hot and cold source.
 8. The device according to claim 1, wherein said at least one inner tube has walls made from at least one thermally insulating material.
 9. The device according to claim 1, wherein said at least one inner tube for discharging said vapour extends into said microporous mass.
 10. The device according to claim 9, wherein said at least one inner tube has an outer wall comprising at least one capillary drain defined by at least one groove, arranged at least on a portion of said inner tube that extends into said microporous mass, so as to convey said liquid phase deep within said microporous mass by capillarity.
 11. The device according to claim 1, wherein said at least one inner tube has an outer wall comprising capillary drains defined for example by grooves, said capillary drains extending over the entire length of said tube.
 12. The device according to claim 1, wherein apart from said microporous mass, an outer wall of said at least one inner tube is in contact with an inner wall of said outer tube, except at the level of at least one capillary drain defining at least one outer duct conveying said liquid phase of said fluid.
 13. The device according to claim 1, wherein said microporous mass has a substantially cylindrical outer shape, together with a portion of said outer tube that houses said microporous mass without radial play.
 14. The device according to claim 1, wherein said evaporator has an area intended to be in heat exchange contact with said heat source and one dimension of said area along an axis of said outer tube is significantly smaller than a length of said microporous mass.
 15. The device according to claim 14, wherein said microporous mass has a diameter and a length that is substantially 2 to 15 times greater than said diameter.
 16. The device according to claim 1, wherein said outer tube is in heat exchange contact with said microporous mass over an outer surface of said mass apart from at least one of longitudinal end surfaces of said mass.
 17. The device according to claim 1, wherein said outer tube has a cross-section with a constant diameter.
 18. The device according to claim 1, wherein said outer tube is made from a good heat conducting material, at least in a first portion of said outer tube that is in heat exchange relationship with said microporous mass, and in a second portion of said outer tube in heat exchange relationship with said condenser or constituting said condenser.
 19. The device according to claim 18, wherein said outer tube is metal, preferably stainless steel.
 20. The device according to claim 1, wherein said outer tube and said at least one inner tube are cylindrical with a circular cross-section, said at least one inner tube having a diameter which is substantially half of a diameter of said outer tube.
 21. The application of a passive thermal regulation device with at least one heat transfer loop according to claim 1, to the transfer of thermal energy from a heat source, such as an electronic component or set of components, in heat exchange relationship with the evaporator, to a cold source, in heat exchange relationship with the condenser.
 22. A method for transferring thermal energy from a heat source to a cold source with a passive thermal regulation device having at least one heat transfer loop, including a step of using a heat transfer loop with capillary pumping of a heat-carrier fluid, said loop comprising an evaporator having a microporous mass, and a condenser, and arranging said evaporator and condenser in heat exchange relationship with a heat source and a cold source respectively, and tubing connecting said evaporator to said condenser and transporting said heat-carrier fluid essentially in vapour phase from said evaporator to said condenser and essentially in liquid phase from said condenser to said evaporator, said tubing comprising an outer tube, housing said microporous mass having a substantially elongated shape and, ensuring a flow of said liquid-phase heat-carrier fluid by capillary pumping, wherein said liquid phase of said fluid is pumped by at least one end of said microporous mass which is facing said condenser, and flows in at least one outer duct delimited between said outer tube and at least one inner tube extending within said outer tube, and said vapour phase of said fluid heated in said microporous mass of said evaporator is collected in a longitudinal central duct made in said microporous mass and discharged by at least one inner duct delimited within said at least one inner tube, said at least one inner tube being connected by one end to an end of said central duct, while said vapour phase is discharged at an other end of said at least one inner tube, at said condenser. 